1. Field of the Invention
The present invention relates to a cooling fan, and more particularly relates to a cooling fan having an improved bearing assembly.
2. Description of Related Art
With the continuing development of the electronic technology, electronic packages such as CPUs (central processing units) are generating more and more heat that requires immediate dissipation. Cooling fans are commonly used in combination with heat sinks for cooling CPUs.
Oftentimes, a cooling fan includes a blade set and a fan seat. The fan seat has a central tube portion integrally formed thereon. A sleeve bearing is arranged in the tube portion. A coil is wound around the outside of the tube portion. The blade set is formed with a hub and fan blades connecting to the hub. A stainless steel rotary shaft supported by the sleeve bearing is arranged within the hub. A magnet pushed by magnetic force of the coil is fixed to the hub and is driven to rotate by the coil so that the fan blades can produce forced airflow. Since the aforesaid stainless steel rotary shaft is arranged to rotatably engage in the sleeve bearing, after rotating for a period of time, the rotary shaft and the bearing will experience wear due to leaking of lubricating oil contained therebetween. Thus, the lifetime of the fan will be reduced.
In order to improve the lifetime of the fan, wear-tolerable ball bearings for point contact have been developed. Each ball bearing has an inner ring, an outer ring and a plurality of balls. The inner ring is mounted on the rotary shaft. The outer ring is connected to the tube portion. The balls are disposed between the inner ring and the outer rings. During operation, the inner ring rotates with the rotary shaft with the support of the balls. In order to make the ball bearing run more smoothly, manufacturing process for the ball bearings requires precision-grinding and a high polish, and thus the ball bearings are more expensive, which results in a high cost.
For the foregoing reasons, therefore, there is a need in the art for a cooling fan which overcomes the above-mentioned problems.